Adhesive Joints with Laser Shaped Surface Microstructures.

One of the most commonly applied methods of joining dissimilar materials is gluing. This could be mainly attributed to the applicability of this technique in various industries. The article presents a method of material surface treatment, which increases the shear strength of adhesive joints for lightweight metals such as aluminum with plastics. For this purpose, laser surface microstructuring was performed on each of the selected construction materials. As a result of the performed treatment, the active surface of the glued area was increased, which increased the adhesive strength. The picosecond laser with UV radiation used in the research is TruMicro 5325c with which material can be removed as a result of the cold ablation phenomenon. The applied parameters of the laser device did not cause thermal damage to the surface of the microstructured materials, which was confirmed by microscopic examination. Laser micromachining did not deteriorate the degree of wetting of the tested materials, either, as was confirmed by the contact angle and surface energy measurements with the use of water as the measuring liquid. In investigated cases of microstructure types, the presented method significantly increased the shear strength of the joints formed, as demonstrated by the presented strength test results. Research has shown that created joints with microstructure made according to the described method, are characterized by a significant increase in strength, up to 376%, compared to materials without microstructure. The presented results are part of a series of tests aimed at selecting the operating laser parameters for the implementation of geometric shapes of microstructures which will increase the strength of adhesive joints in selected materials.

Imaging and emission spectroscopy of the submicrosecond plasma generated from copper substrate with nanosecond laser pulses.

In this paper, an experimental investigation of the ablation plasma generated from the copper substrate by means of nanosecond laser pulses is presented. We studied the evolution of the ablation plasma in the first 1000 ns after plasma onset using the fast-gated imaging and optical emission spectroscopy methods. Plasma imaging showed that the expansion of the plume front can be described using a so-called drag model, with the expansion limit increasing with laser fluence from 254 µm for 30J/cm2 to 375 µm for 67J/cm2. By using the Boltzmann plot and Stark broadening methods, it was found that within the first microsecond after onset, the electron excitation temperature and electron number density decrease from 1.2 eV to 0.8 eV and from 4×1016cm-3 to 5×1015cm-3, respectively. Using the McWhirter criterion, we confirmed that in the considered time range the plasma remains in a state of local thermodynamic equilibrium.

Measurement of OH radicals distribution in a microwave plasma sheet using LIF method.

Microwave plasma sources (MPSs) operating at atmospheric pressure provide plasmas in the form of a flame or cylindrical column. In contrast, this article presents an innovative MPS (patented by us) for generating a new type of plasma, i.e. in the form of a plasma sheet, which is generated in a flat cuboidal quartz box. It is based on a WR 340 waveguide, powered by microwaves of 2.45 GHz and operated in argon at atmospheric pressure. The plasma sheet contains a multitude of filaments typical of microwave argon plasmas. In the presented experiment, the spatial distribution of the OH radicals in the microwave plasma sheet was measured by means of the LIF method. Studies have shown that the relative concentration of OH radicals increases with the increase in microwave power and decreases with the increasing argon flow rate.